This application is related to U.S. application Ser. Nos. 07/632,880; 07/632,881; 07/632,882; 07/632,883; 07/633,703; 07/633,704; 07/633,738; 07/633,739; 07/633,743; 07/633,744; Dec. 24, 1990, all assigned to the assignee of this application, and all incorporated herein by reference.
This invention relates to synchronizer mechanisms for a transmission. More specifically, the invention relates to such mechanisms of the self-energizing type with means to limit self-energizing force.
It is well known in the multiple ratio transmission art that synchronizer mechanisms may be used to reduce shift time of all or some of the transmission gear ratios. It is also known that the shift effort required by a vehicle operator, i.e., force applied to a shift lever, may be reduced by use of synchronizer mechanisms of the self-energizing type. Since operator shift effort generally increases with vehicle size and weight, synchronizer mechanisms of the self-energizing type are especially important for heavy duty trucks. Prior art examples of such mechanisms may be seen by reference to U.S. Pat. Nos. 2,410,511; 2,896,760; 3,548,983; 4,413,715; 4,836,348; and 4,869,353 which are incorporated herein by reference.
The synchronizer mechanisms of the above patents include friction and jaw members for respectively synchronizing and positive clutching a gear to a shaft; blockers engaged in response to a pre-energizer effecting initial engagement of the friction members in response to initial engaging movement of one of the jaw members by a shift force, the blockers being operative to prevent asynchronous engagement of the jaw members and to transmit the shift force to the friction members to increase synchronizing torque thereof; and self-energizing ramps reacting the torque to provide an additional force in the direction of an additive to the shift force for further increasing the synchronizing torque of the friction members.
The basic purpose of such self-energizing synchronizer mechanisms is of course to provide faster synchronizing times with relatively moderate shift force from a manually operated shift lever for example. For a given synchronizer mechanism geometry and shift force, the additional force may be varied by varying the angles of the self-energizing ramps. In theory, ideal ramp angles exist which produce maximum controllable additional forces. For the frame of ramp angle references herein, the additional forces decreases as the ramp angles increase. Ramp angles less than the ideal angles produce uncontrollable additional forces, which once initiated, rapidly increase independent of the shift force and quickly drive the cone clutch to a lock-up condition. Ramp angles producing uncontrollable additional forces are said to be self-locking rather than self-energizing. Self-locking decreases shift quality or feel, may over stress synchronizer and other components, may cause overheating and rapid wear of the cone clutch surfaces, and may even override operator movement of the shift lever.
In practice the so called ideal ramp angles may vary substantially due to any of several variables, e.g., coefficient of friction variations, ramp surface wear, manufacturing tolerances, etc.
An object of this invention is to provide a self-energizing synchronizer mechanism which limits the additional forces produced by self-energizing ramps.
According to a feature of the invention, a self-energizing synchronizer mechanism is provided for a first gear secured against axial movement on a shaft having an axis about which the gear and shaft rotate relative to each other. The mechanism comprises: first friction and jaw means drivingly connected to the shaft and respectively engagable with friction and jaw means affixed to the first gear for respectively synchronizing and positive connecting the first gear to the shaft in response to a shift force axially directed toward the first gear moving a shift means toward the first gear; first and second blocker means operative when engaged for preventing engagement of the jaw means prior to the synchronizing; pre-energizer means for engaging the friction means in response to initial axial movement of the shift means by the shift force from a neutral position toward the first gear, for engaging the blocker means in response to engagement of the friction means producing an initial synchronizing torque, and for transmitting the shift force to the first friction means via the blocker means to increase the engaging force of the friction means; and first self-energizing means including first and second ramp means engagable in response to synchronizer torque in one direction for reacting the synchronizing torque between the friction means and the shaft and for producing an axial additional force which further increases the force engaging the first friction means.
The improvement is characterized by resilient means for limiting the additional force.